This invention relates generally to rotating anodes for x-ray tube targets and, more particularly, to a molybdenum alloy substrate for an anode with improved means for attachment to an x-ray tube stem.
In the historical development of a rotating anode for x-ray tubes, manufacturers have progressed from the use of a tungsten substrate material to that of a molybdenum material, and finally to that of a molybdenum alloy material. The pure molybdenum material was found to have a thermal capacity substantially equal to that of tungsten but also offered the attractive advantage of being a relatively low density material which allowed the use of bigger targets. On the negative side, however, it was found to be susceptible to thermal creep which caused eventual warpage of the target. This problem was initially addressed with the use of a five percent tungsten additive to the molybdenum to provide higher strength. That was followed by the introduction of the so-called dispersion-strengthened molybdenum alloy materials presently in use. One such high-strength material is that described in U.S. Pat. No. 4,195,247, issued on Mar. 25, 1980 and assigned to the assignee of the present invention. Another such material is that known as TZM (titanium, zirconium and molybdenum, as well as carbon) which is commercially available from Metallwerk Plansee Aktiengesellschaft.
The rotatable anode has traditionally been attached to the stem of an x-ray tube rotor by such means as a mechanical attachment, welding, or diffusion bonding. Since the stem is normally composed of a different material from that of the target, an adequate attachment by way of diffusion bonding is difficult to obtain. For example, a desirable material for use in the stem has been found to be columbium, because of its relative high strength and low thermal conductivity. While a columbium stem is compatible with both a pure molybdenum target and a molybdenum/tungstem target for purposes of diffusion bonding, it has been found to be relatively incompatible for diffusion bonding to the dispersion-strengthened molybdenum alloys.
It is therefore an object of the present invention to provide an improved means of attaching a molybdenum alloy x-ray anode to a stem of a different material.
Another object is to provide a means of diffusion bonding a molybdenum alloy anode to a stem composed of a different material.
Yet another object is to provide a diffusion-bonded anode which is economical to manufacture and effective in use.
These objects and other features and advantages become more readily apparent upon reference of the following description when taken in conjunction with the appended drawings.